1. Field of the Invention.
The invention relates to the field of computer-aided design and more particular to the implementation of simulation algorithms.
2. Prior Art.
In the last ten years, computer-aided design has become commonly used in many fields, such as in the design of electrical circuits. Indeed, today it would be difficult and perhaps economically impossible, to develop a large scale integrated circuit without verification design tools. The "bread boarding" of a circuit having a million components would be a monumental task and equally impractical would be the continual revision to masks required if the circuit were not verified before fabrication.
Numerous work stations or other tools are currently available for simulating systems. The present invention is used in conjunction with one of these commercially available work stations sold under the trademark "Logician" by Daisy Systems Corporation of Sunnyvale, Calif. This prior art system and the algorithm which it implements will be discussed in conjunction with FIGS. 1, 3 and 4. In general, the present invention implements an event driven simulation algorithm in a special purpose computer.
The closest prior art reference known to the Applicant disclosing special purpose computers for implementing simulation algorithms are:
(i) "A Logic Simulation Machine" by Abramovici, M. Et Al, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems Vol. CAD-2, No. 2, April 1983. The present invention implements an algorithm similar to that described in this article. However, the partitioning used in the present invention is substantially different than that discussed in the article.
(ii) "ZYCAD Logic Evaluator" as described in ZYCAD Corporation's manual dated November, 1982. This apparatus employs different partitioning than the present invention. Moreover, it does not offer the flexibility of the presently described invention where the computer is microcode programmable.
(iii) "Parallel Processing Interactively Simulates Complex VSLI Logic" by Howard, J. Et Al, Electronics Dec. 15, 1983, beginning at p. 147. This article describes the implementation of a different algorithm which is not event driven. Different architecture and partitioning are employed. (Applicant does not concede that this particular article is prior art, however, Applicant believes that there are prior art computers employing the teachings of this article.)